[ruby-core:104981] [Ruby master Feature#18083] Capture error in ensure block.

Issue #18083 has been updated by duerst (Martin D=FCrst).


Eregon (Benoit Daloze) wrote in #note-3:
> If you only need to know if there is an `Exception` this seems easier:
> Using the example from https://bugs.ruby-lang.org/issues/15567#note-27
> ```ruby
> begin
>   ...
> rescue Exception =3D> exception
>   transaction.abort
>   raise exception
> ensure
>   transaction.commmit unless transaction.aborted?
> end
> ```

What about
```ruby
begin
  ...
rescue Exception
  transaction.abort
else
  transaction.commit
end
```
It seems shorter and easier to understand.

Having read through most of #15567, my impression is that:
- Ruby already has too many features for exceptional flow control. Adding m=
ore stuff that makes this even more complicated doesn't look like an improv=
ement of the language. (Go To Statement Considered Harmful, anybody?)
- All the documentation/books that I can remember explain Exceptions and ca=
tch/throw completely separately (although usually in close proximity, becau=
se both features don't really fit anywhere). Some improvement seems in orde=
r, even if this is only "don't use them together".
- `ensure` contains always executed code. Adding conditions to its syntax s=
eems strange. It would be similar to extending the syntax of `else` (both i=
n `if` expressions as well as in `begin` blocks). Specific conditions shoul=
d be handled where we already have them, on `rescue`, e.g. like `rescue whe=
n throw` or some such (if at all).
- The argument that Rubocop complains about something isn't really an argum=
ent. If Rubocop is wrong, it should be fixed.


----------------------------------------
Feature #18083: Capture error in ensure block.
https://bugs.ruby-lang.org/issues/18083#change-93381

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
As discussed in https://bugs.ruby-lang.org/issues/15567 there are some tric=
ky edge cases.

As a general model, something like the following would be incredibly useful:

``` ruby
begin
 ...
ensure =3D> error
  pp "error occurred" if error
end
```

Currently you can get similar behaviour like this:

``` ruby
begin
  ...
rescue Exception =3D> error
  raise
ensure
  pp "error occurred" if error
end
```

The limitation of this approach is it only works if you don't need any othe=
r `rescue` clause. Otherwise, it may not work as expected or require extra =
care. Also, Rubocop will complain about it.

Using `$!` can be buggy if you call some method from `rescue` or `ensure` c=
lause, since it would be set already. It was discussed extensively in https=
://bugs.ruby-lang.org/issues/15567 if you want more details.



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